Passively cooled, high concentration photovoltaic solar cell package

ABSTRACT

The solar cell modular unit has a minimal number of components each of which are easily manufactured and which also have a relatively economical cost. It has a laminar substrate having an electrically conductive layer on its top surface that includes the printed electrical circuit. The middle layer is heat conductive and not electrically conductive. The bottom layer is made of thermally conductive material. A solar cell is centrally mounted on the printed circuit board. A base assembly covers the solar cell and it has a vertical tunnel extending from its top surface to the solar cell. An elongated sun shield has an aperture in its top panel that aligns with the tunnel of the base assembly. The sun shield snap-locks onto the top of the base assembly. A secondary optical element telescopically mates with the aperture in the sun shield and the tunnel of the base assembly. A primary light ray refractive member is positioned at a predetermined spaced location above the SOE.

This application claims priority of U.S. Provisional Patent ApplicationNo. 60/714,599 filed Sep. 7, 2005.

BACKGROUND

1. Field of Invention

The present invention relates to the design and assembly of a singlephotovoltaic modular unit and ancillary hardware into a modular packagefor use under highly concentrated sunlight to convert sunlight toelectricity reliably and inexpensively.

2. Prior Art

In traditional one-sun solar panels, photovoltaic devices are tightlypacked or coated onto a flat substrate to capture the radiationimpinging on the surface. The cells are interconnected electrically andthe entire unit is encapsulated to protect it from terrestrial elements.The tightly packaged cells minimize the area not covered by thephotovoltaic material, making interconnection simple and encapsulationefficient. To make photovoltaics competitive with other energy sources,the cost of the system must come down. Since the photovoltaic materialcan be 50% or more of the system costs, one method to reduce this costis to minimize the amount of photovoltaic material by concentrating thesolar energy to a smaller area using refractive or reflective means.This method can require individual receiver packages for each solar cellto further decrease the material costs. The smaller discrete packageshowever, come with concomitant disadvantages including such things asincreased difficulty in interconnection, encapsulation, mechanicalalignment, and thermal management requirements associated with highconcentration photovoltaics.

The requirements of such packages are typically at least as stringent asthose seen in one-sun applications.

1. There is the requirement of high voltage isolation from groundpotential (near 2000 VDC).

2. There is the need for the protection of any active electrical partsfrom moisture and the elements.

3. There is the need to dissipate a higher localized heat load presenton the small photovoltaic cell due to high radiation fluxes intrinsic toconcentrating the sunlight.

4. There is the need for all parts of the receiving unit to withstandhighly concentrated sunlight either through a prudent choice ofmaterials or a protective element in case on any errors in tracking.

5. There is the need to accurately redirect errant rays from the primaryconcentrator onto the cell due to concentrator manufacturing tolerances,imaging alignment errors, or sun tracking errors.

Prior attempts to meet all of these requirements have involved eitherexpensive materials or many different parts, with a complex andexpensive assembly process. Yields and throughput have suffered as aresult. Reliability problems also have resulted due in part to the highpiece part count.

SUMMARY OF THE INVENTION

The principal object of the present invention is to meet the variedrequirements of a cell package under concentrated sunlight in anintegrated manner. It secondarily allows for efficient manufacturabilityand assembly of the package ultimately bringing the cost of the systemdown.

The package consists of a thermally conductive material with highdielectric strength, laminated to a thermally conductive substrate onthe bottom and to an electrically conductive layer on the top for thetransport of the generated carriers. The substrate is of laminateconstruction allowing for the use of common printed circuit boardtechnology widely available in many parts of the world. The dielectricsis highly thermally conductive allowing for a temperature rise across itof less than 10 degrees C. under operating conditions of 20 W/cm2. Thelower temperatures not only increases the power output of a solar cell,but also extends its reliability. This substrate is then attached to aheat spreader that doubles as a structural element for optimal heatdissipation.

On the topside of the cell, a secondary optical element (SOE) isattached to or suspended above the substrate to capture the rays notfocused by the primary element onto the cell. This primary element cantake the form of a refractive element that bends the rays back onto thecell, or a reflective element that reflects errant rays back onto thecell. The element is correctly aligned with the lens and cell opticalpath through alignment pins fabricated into a holding base and holesfabricated into the substrate. This holding base is made frominexpensive material and also integrates the sealing function to helpmeet the moisture intrusion requirements. The base also allows for asimple interface with the protective element that covers any sensitiveareas of the receiving unit to concentrated sunlight in the case oftracking error or loss. This protective sun-shield is made from amaterial that can accommodate the high fluxes and/or temperaturesgenerated by concentrated sunlight. These might include materials suchas aluminum, aluminized polymers, mirrored glass, ceramic, porcelain,clay, or fiberglass. Again, the sunshield has the ability to interfacewith the integrated SOE base/cowling in a snap fit for ease of assemblyof the SOE.

This invention takes the various components and assembles them in a waythat is more conducive to mass production. It allows for easy assemblyof the entire package with minimal use of adhesives or fasteners byusing “snap-fits” between many of the parts. This saves costs in bothpart numbers and assembly time. The substrate uses printed circuit boardtechnology for ease of technology transfer between vendors and for easeof modification without any hard tooling costs. The secondary opticalelement utilizes a highly reflective material shaped to take advantageof cheap manufacturing methods. The SOE base has high tolerancealignment pins that register to the substrate to ensure proper alignmentof the optical element to the cell. It secondarily acts to seal thepackage from water intrusion should moisture ever enter the module. Italso allows for a snap-fit with the sunshield. Finally, the substrate isattached to the structural element which doubles as a heat spreader. Aheat sink behind to enhance thermal dissipation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view showing several solar arrays thatutilize the solar modular unit;

FIG. 2 shows one of the solar units of the solar array illustrated inFIG. 1;

FIG. 3 is an exploded schematic view of the structure illustrated inFIG. 2;

FIG. 4 is an exploded perspective view of the solar cell modular unit;

FIG. 5 is an exploded perspective view showing the position between arefractive primary element and a receiver plate upon which the solarcell modular unit is fastened;

FIG. 6 is a cross sectional view of the substrate;

FIG. 7 is a top perspective view of the substrate showing the solar cellsoldered onto the printed circuit board;

FIG. 8 is a top perspective view of the base assembly;

FIG. 9 is a bottom perspective view of the base assembly;

FIG. 10 is a bottom perspective view of the sun shield showing a pair ofsolar cell modular units installed therein;

FIG. 11 is a schematic side elevation view showing the receiver snaplocked onto the base assembly;

FIG. 12 is a top perspective view illustrating the manner in which thesecondary optical element is attached to the sun shield; and

FIG. 13 is a top perspective view showing a pair of secondary opticalelements installed in the sun shield.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention will now be discussed by referring to FIGS. 1-13 of thedrawings. FIG. 1 is a front perspective view illustrating several solarpower arrays 20. FIG. 2 shows one of the solar units 22 of the solararray. FIG. 3 is an exploded schematic view of FIG. 2 showing a Fresnellens porquet 24 having multiple Fresnel lenses 26. The Fresnel lensporquet 24 is mounted on the top of compartment 28. Inside compartment28 is a receiver plate 30 mounted on a heat sink 32. A plurality of sunshield strips 34 have individual solar cells 36 mounted on them.

One of the solar cell modular units 40 is illustrated in FIG. 4. Asubstrate 42 has an electrical printed circuit on the top surfacethereof. Solar cell 36 is soldered on the printed circuit. A baseassembly 44 is mounted over solar cell 36. A sun shield strip 34 is snaplocked onto the top of base assembly 44. The secondary optical element(SOE) 46 telescopically passes through cut-out 48 and into the top endof base assembly 44. FIG. 5 shows one of the Fresnel lens 26 spacedabove SOE 46. Base assembly 44 is fastened by screws through substrate42 to receiver plate 30. Receiver plate 30 is mounted on the top of heatsink 32.

Substrate 42 is illustrated in FIG. 6. It has an electrically conductivetop layer 50, a heat conductive layer 52 that is not electricallyconductive and a bottom thermally conductive layer 54. FIG. 7 shows asolar cell 36 soldered to the top of the electrical printed circuit onlayer 50 of substrate 42. Apertures 56 receive screws that are insertedthrough aligned apertures in base assembly 44 and the screws aretightened into receiver plate 30. L-shaped conductor terminals 58 aresoldered to the top surface of the electrical printed circuit.

Base assembly 44 is best illustrated in FIGS. 8 and 9. It has a baseplate 60 having a top surface 61 and a bottom surface 62. A tower member64 extends upwardly from base plate 60. A tunnel 66 extends downwardlyfrom the top end of tower member 64 to the bottom surface of base plate60. Tunnel 66 has a top opening 68 and a bottom opening 67. Top opening68 is larger than bottom opening 67 and the respective side walls oftunnel 66 are tapered from its top end to its bottom end. A pair ofwings 70 extend downwardly and outwardly from the top end of towermember 64. A pair of boss members 72 extend upwardly form the topsurface of base plate 60. FIG. 9 shows a pair of alignment pins 74 thatare designed to mate with the substrate for accurate alignment of theSOE 46 to the solar cell 36. A slot 74 is on each side of tower member64 and each receives one of the L-shaped conductor terminals 58.

FIG. 10 is a bottom perspective view of the sun shield 34 showing a pairof solar cell modular units 40 installed therein. FIG. 11 shows themanner in which the sun shield snaps on to the top of base assembly 44.Sun shield 34 has a top panel 80 having resilient arms 82 extendingdownwardly from its lateral sides. They snap over wings 70 of baseassembly 44. FIGS. 12 and 13 show the structure of SOE's 46 mating withtop panel 80 of sun shield 34. Tabs 86 mate with slots 88 to provide aneasy method of assembly and also to provide a positive lockingstructure.

Although this invention has been described in connection with specificforms and embodiments thereof, it will be appreciated that variousmodifications other than those discussed above may be resorted towithout departing from the spirit or scope of the invention. Forexample, equivalent elements may be substituted for those specificallyshown and described, certain features may be used independently of otherfeatures, and the number and configuration of various componentsdescribed above may be altered, all without departing from the spirit orscope of the invention as defined in the appended Claims.

1. A solar cell modular unit comprising: a substrate having a topsurface and a bottom surface; an electrical printed circuit is formed onsaid top surface; a solar cell mounted on the top surface of thesubstrate, the solar cell having a top surface and a bottom surface;means for connecting said bottom surface of said solar cell to saidelectrical printed circuit on said top surface of said substrate; a baseassembly mounted to the top surface of the substrate comprising: a baseplate having a top surface and a bottom surface, the bottom surfacemounted to the top surface of the substrate, a tower member having a topend and a bottom end, said bottom end of the tower member beingconnected to said top surface of said base plate, a tunnel extendsdownwardly from said top end of said tower member to said bottom surfaceof said base plate, said tower member having a top opening having apredetermined configuration and a bottom opening having a predeterminedconfiguration, said top opening being larger than said bottom opening,said tunnel being defined by tapered side walls disposed between saidtop opening and said bottom opening; a tapered tubular secondary opticalelement (SOE) having a top end, a bottom end, surrounding side wallsextending from said top end to said bottom end, said side walls havingan inner surface defining a top opening and a bottom opening and saidtop opening being larger than said bottom opening; and said bottom endof said tapered tubular SOE being telescopically received in said tunnelof said tower member, the bottom end of the tapered tubular SOEcooperating with the tapered side walls of the tunnel to align the SOEto the solar cell while said top end of said tapered tubular SOE remainsoutside of said tunnel of said tower member.
 2. A solar cell modularunit as recited in claim 1 wherein said substrate has laminar structurehaving an electrically conductive top layer, a central layer of heatconductive material that is not electrically conductive and a bottomlayer of thermally conductive material having a high dielectricstrength.
 3. A solar cell modular unit as recited in claim 2 whereinsaid substrate has four side edges and four corners.
 4. A solar cellmodular unit as recited in claim 1 wherein said solar cell is siliconsolar cell.
 5. A solar cell modular unit as recited in claim 1 whereinsaid means connecting said solar cell to said electrical printed circuitis solder material.
 6. A solar cell modular unit as recited in claim 1wherein said base plate and said tower member are an integrally formedstructure.
 7. A solar cell modular unit as recited in claim 6 whereinsaid integrally formed structure is made of molded plastic material. 8.A solar cell modular unit as recited in claim 6 wherein said base platehas four side edges and four corners.
 9. A solar cell modular unit asrecited in claim 8 wherein said base plate and said substrate havesubstantially the same configuration.
 10. A solar cell modular unit asrecited in claim 1 wherein said inner surface of said side walls of saidtubular SOE have reflective properties for directing light rays towardsaid solar cell.
 11. A solar cell modular unit as recited in claim 10wherein said bottom opening of said tubular SOE and said solar cell havesubstantially the same configuration.
 12. A solar cell modular unit asrecited in claim 11 wherein said bottom opening of said SOE and saidsolar cell each have four side edges and four corners.
 13. A solar cellmodular unit as recited in claim 1 further comprising a receiver platehaving a top surface and a bottom surface and said substrate is securedto said top surface of said receiver plate by fastener means.
 14. Asolar cell modular unit as recited in claim 13 further comprising anelongated heat sink member having a top surface, wherein the top surfaceof said heat sink member is secured to said bottom surface of saidreceiver plate.
 15. A solar cell modular unit as recited in claim 14wherein the vertical cross section of said heat sink member has ahat-shaped configuration.
 16. A solar cell modular unit as recited inclaim 1 further comprising an elongated sun shield mounted over the baseplate and tower member and having a vertical cross section having ahat-shaped configuration that has a top panel having lateral side edgesfrom which extend resilient arms.
 17. A solar cell modular unit asrecited in claim 16 wherein said top end of said tower member of saidbase assembly has structure for allowing said resilient arms of said sunshield to be detachably snap-locked to said structure.
 18. A solar cellmodular unit as recited in claim 16 wherein said top panel of said sunshield has a cut-out aperture configured to telescopically receive thebottom end of said tubular SOE.
 19. A solar cell modular unit as recitedin claim 1 wherein the tower member further comprises a wing extendingoutwardly, the wing configured to engage a heat sink member to securethe heat sink member in a predetermined position in relation to thetower.
 20. A solar cell modular unit as recited in claim 1 wherein thetower member further comprises a plurality of slots located between thetop end of the tower member and the base plate, each slot configured toreceive an electrical conductor for contact with the circuit of thesubstrate.
 21. A solar cell modular unit as recited in claim 1 whereinthe tunnel comprises a shape that corresponds to the SOE such that whenthe SOE is received by the tunnel, the tunnel confines the SOE to apredetermined position at which the bottom opening of the SOE faces thesolar cell, whereby energy entering the SOE is directed to the solarcell.
 22. A solar cell modular unit as recited in claim 1 wherein saidbottom end of said tower member has a bottom surface mounted on saidbase plate.
 23. A solar cell modular unit as recited in claim 1 whereina configuration of said tapered tubular SOE corresponds directly with aconfiguration of said tapered side walls of said tunnel to independentlyalign said SOE to said solar cell.
 24. A solar cell modular unit asrecited in claim 1 further comprising one or more alignment pins on saidbase assembly that register to said substrate to ensure proper alignmentof said SOE to said solar cell.